I was in the middle of writing more on my CoCo Base-64 encoding series and stumbled upon some weirdness with the DATA command. Consider this silly program:
0 REM baddata.bas
10 READ A$:IF A$="" THEN END
15 PRINT A$;:GOTO 10
20 DATA ":"
30 DATA HELLO
40 DATA ""
This will print:
:HELLO
I know I could just have done DATA “:HELLO” but stay with me on this..
If you try to combine lines like this:
0 REM baddata.bas
10 READ A$:IF A$="" THEN END
15 PRINT A$;:GOTO 10
20 DATA ":":DATA HELLO
40 DATA ""
…you get this:
Color BASIC DATA quirk.
When I get a moment, I’ll have to look at the ROM disassembly and see what is going on.
In C, “#ifdef” or “#if defined()” are used to hide or include portions of code only if certain conditions are met. For example, my recent *ALL RAM* BBS experiment contains code for using the SD card library as well as the Ethernet library. I used #ifdef around specific blocks of code so I could compile versions with or without either of those libraries. But all is not well in Arduino land. Consider this following, simple example:
In this example, I did not want the fileReadln() function to be included unless I had defined FOO. But, compiling this produces:
ifdef:15: error: ‘File’ was not declared in this scope
ifdef:15: error: expected primary-expression before ‘char’
ifdef:15: error: expected primary-expression before ‘count’
ifdef:15: error: initializer expression list treated as compound expression
Unhelpful. And after wasting some time on this, I started a topic in the Arduino.cc forums to ask if others were experiencing the same thing. And they were. A helpful post from parajew pointed me to this site which helped explain the problem, and offered a workaround:
http://www.a-control.de/arduino-fehler/?lang=en
The pre-processor does some stuff behind the scenes, creating prototypes and including header files where needed, and it just does it wrong. The A-Control site figured out a simple workaround, which I trimmed a bit to just adding this at the top of my scripts:
// BOF preprocessor bug prevent - insert me on top of your arduino-code
// From: http://www.a-control.de/arduino-fehler/?lang=en
#if 1
__asm volatile ("nop");
#endif
…and now either of my examples will compile as intended. Thank you, parajew and A-Control! I can now move on to my next problem…